In a conventional brake system of the automobile, friction created when a brake shoe is pushed to a brake drum will suddenly stop a rapidly rotating wheel, and another friction created thereby between a round tire and a road surface will stop the automobile. In this case the contact between the tire and the road surface is, so to speak, a linear contact, Thus, it requires a long distance during which the automobile stops because of an insufficient friction created between the tire and the road surface. Besides, in the case of a four-wheel vehicle, it is difficult to allow the four wheels to stop completely at the same time. Thus, there are differences in time before each wheel stops completely, and this causes the tires to slip sideways. These are the defects of the conventional brake system.
As the speed of automobiles becomes faster and highways are crowded with vehicles, a long brake stopping distance may cause an automobile to collide against another from behind, and an automobile slipping sideways causes it to be overthrown.